Home |
Search |
Today's Posts |
|
#1
![]() |
|||
|
|||
![]()
Tom Horne wrote:
On Apr 8, 2:16 pm, Jim Lux wrote: Tom Horne wrote: I am interested in having a rapid set up multi-band vertical for Field Day and EMCOMM. If I use the Hy-Gain sixty four foot (64') push up mast as the radiator and an ICOM AH-4 as the automatic antenna tuner is this likely to be an effective approach to having a rapid set up multi band vertical? Yes.. You don't need that much height, though.. the loss in radiation effectiveness going from 1/4 wavelength (20m long) to 1/8 wavelength (10m) isn't all that big a deal. It's when you get down to the 1/20th wavelength and the feedpoint Z gets very wild that you have problems with loss in the matching network. Will I need radials? Should they be elevated or can they lie on the ground? Yes.. you do need radials. Laying on the ground is just fine. Get some very flexible stranded insulated wire (the kind with lots of fine strands is better.) and figure a way to rapidly throw it out and store without tangling. I've thought about spring return reels. 3 or 4 makes a huge difference over 1 or 2. after that, it's a bit of diminishing returns.. You'd be better off just doing what the people who do this for a living (rapid deploy HF comms) do.. jack up the Tx power. BTW, a better approach than a vertical might be a inverted V dipole from the top of your 60 foot pole. MUCH better radiation effectiveness because of H polarization.. Since the total length of the radiator is less than a 1/4 wave on eighty meters at say 3.6 MHz will that make the antenna ineffective on eighty meters? Nope.. it's the loss in the tuning network that's the thing to worry about.. you could make a lumped matching network to feed with your autotuner if you're worried.. Second question would four of those sixty four foot masts make an effective forty meter four square. Yes I realize that it would cost eight hundred dollars for the masts alone before the cost of controller, remote, phasing coax, and control cable. Once again would radials be required for forty meters. Radials are (almost) always required for verticals. even if you don't install them, your feedline shield will act as a radial with unpredictable and usually undesirable effects. Running a 4 square with autotuners at each element is VERY difficult (if not impossible).. the tuner changes the phase shift, and the interaction from the other antennas will screw up the auto adjustment algorithm. I've only been back in radio for a few years after very long gap so I'm starting over and finding the learning curve a little steeper than I remember. -- Tom Horne, W3TDH Jim I had no intention of running a four square with four auto tuners. Perhaps I should have put that inquiry into a separate posting for the sake of clarity. We built a four square for field day two years ago. Because the masts that we had then were only thirty feet high a kind of capacitance hat was built into the guy lines. We had very good performance from that four square until a severe thunderstorm destroyed it. I was wondering if having sixty four foot masts would allow us to adjust the height to resonance on forty meters so that the four masts themselves could serve as the elements of the four square. Since a half wave at 7150 kHz is nearly sixty seven feet I would have to add three feet worth of additional tubing in order to get a resonant half wave antenna. I had thought that half wave verticals did not require a counterpoise was I misinformed? If a counterpoise is needed it wouldn't be too hard to throw out four radials for each mast. I was just looking for a quick way to put up a four square and these aluminum masts seemed like they might fill the bill. Tom, is this a serious exercise here? This is just way too much trouble for a 40 meter antenna. Some antennas like the half wave verticals, don't require radials. But I see a vacillating back and forth between high performance and well, these verticals, which really aren't High performance. As for several 64 foot masts, Why not go to one mast and put up a 40 meter beam beam? Add an Amp, and you will rule the air. Although I wouldn't do that personally, because I would imagine that the idea of emergency ops is getting set up and running ASAP. It could be a matter of temperament I guess. You can get most of your needed performance out of a simple dipole. But if you want to wring the last drop of performance, I'd have to think the beam would take less time to set up and perform better than a 4-square. You don't want to finish installing and tuning just at the time they send everyone home. - 73 de Mike N3LI - |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
![]() |
||||
Thread | Forum | |||
Where does high gain antenna get the gain from? | Antenna | |||
Wire Antenna Element s : Five Foot (5') Long -=V=- Fifty Foot (50') Long | Shortwave | |||
FREE Birdview Dish's 9 foot and 10 foot | Boatanchors | |||
Hy-Gain Hy-Tower 2" Mast Needed | Antenna |